Non-silver direct positive dye bleachout system using indigoid dyes and colored activators

ABSTRACT

A DIRECT POSITIVE BLEACH-OUT PHOTOGRAPHIC SYSTEM SUITBLE FOR PHOTOGRAPHY AND PHOTOCOPY WORK. AN INDIGOID DYE AND A COLORED ACTIVATOR, SUPPORTED IN A BINDER, FORM THE PHOTOSENSITIVE SYSTEM WHICH IS BLEACHED OUT WHEN EXPOSED TO VISBILE LIGHT. A FEW ARE SENSITIVE TO ULTRAVIOLET LIGHT. THE SYSTEM IS ADAPTED TO FORMING PRINTS AND TRANSPARENCIES IN BLACK AND WHITE, MONOCHROME AND FULL COLOR.

Jly 27, 19M J c GERLACH ETAL 595 65" xowmmvm DIRECT POSITIVE DYEBLEACHOUT SYSTEM USING INDIGOID DYES AND COLORED ACTIVATORS 2Sheets-Sheet Filed 001;. 3, i968 II" II!" INVENTORS w M A mN R m J Gm 0O H E m m N E mK V. B

ATTORNEY J. c. GERLACH ET AL 3,595,659

July 27, 1971 NON-SILVER DIRECT POSITIVE DYE BLEACH-OUT SYSTEM usmcINDIGOID DYES AND COLORED ACTIVATORS 2 Sheets-Sheet 3 Filed Oct. 5, 1968EXPOSURE WHITE LIGHT 4o nnnnnufl' WHITELIGHT #lmllllli BLUE GREEN REDTRANSMITTED FIG. H

iliiuiiiinl INVENTOE JOANNE C. GERLACH IAN D. ROBINSON BY KENNETH D.JORDAN ATTUEW United States Paten 1.3::

11.5. CI. 9648 19 Claims ABSTRACT OF THE DISCLOSURE A direct positivebleach-out photographic system suitable for photography and photocopywork. An indigoid dye and a colored activator, supported in a binder,form the photosensitive system which is bleached out when exposed tovisible light. A few are sensitive to ultraviolet light. The system isadapted to forming prints and transparencies in black and white,monochrome and full color.

CROSS-REFERENCES TO RELATED APPLICATIONS In four copending applicationswe have disclosed four other direct positive bleach-out systems. Theseapplications are Ser. No. 764,661 filed Oct. 3, 1968 directed to acombination of polymethine dyes and essentially colorless activators;Ser. No. 764,662 filed Oct. 3, 1968 directed to a combination ofpolymethine dyes and colored activators; Ser. No. 764,744 filed Oct. 3,1968 directed to a combination of indigoid dyes and essentiallycolorless activators; and Ser. No. 764,742 filed Oct. 3, 1968 directedto a combination of stable free radical dyes and essentially colorlessactivators.

This invention relates to a photographic method and article and moreparticularly to a direct positive bleachout photographic system suitablefor photography to produce black-and-white, monochrome and full colorprints and transparencies, for photocopying to make black-andwhite,monochrome and full color copies and to processes and articles whichinvolve as at least one step or product the making of a photographiccopy.

There is, of course, a large body of prior art concerned with thegeneral fields of photography and photocopying. This body of prior artincludes the use of silver halide emulsions with their attendantdarkroom processing techniques, the employedment of photoconductiveparticles or films with accompanying formation of electrostatic latentimages and subsequent toning and fixing, and the formation of vesicularimages in water-in-sensitive photographic materials. However, sincethese prior art techniques are completely distinguishable from that ofthe present invention, they need not be discussed. Rather, the prior artwhich is pertinent to this invention is set forth in a series of UnitedStates patents (see for example USP 3,102,027, 3,104,973, 3,114,635,3,154,416 and 3,155,509) describing a so-called bleach-out systememploying a light-sensitive combination of a dye and an activator.Exposure of these light-sensitive materials effects bleaching of thedyes in those areas exposed to light of a predetermined wavelengthrange. The unexposed areas remain the color of the original dye, thusforming a contrast which gives rise to a copy or photograph.

Bleach-out systems of this type have certain marked advantages, amongwhich may be listed the absence of graininess, the elimination ofdarkroom procedures and rapidity of access. However, the prior artsystem, although realizing these advantages at least in part, possesscertain inherent disadvantages. As activators for the dye systems, theprior art uses an alkyl, aryl, or aralkyl compound having at least threehalogen (Cl, Br, or I) atoms attached to a single carbon atom, e.g., CBrThese activators are highly toxic and noxious to use. Moreover, some ofthe light-sensitive systems of the prior art show a marked tendency todevelop color in the bleached areas during use or storage even in theabsence of light, thus causing eventual obliteration of the copy. Mostof these prior art systems cannot be fixed satisfactorily.

It would, therefore, be desirable to have a positive bleach-outphotographic system which retained all the advantages inherent in such asystem and which at the same time is capable of overcoming at least someof the more restrictive disadvantages associated with the prior artsystems.

It is therefore a primary object of this invention to provide alight-sensitive, positive bleach-out photographic system which iscapable of providing a sharp, positive grainless copy of rapid accesswhich exhibits improved stability. It is another object of thisinvention to provide a light-sensitive system of the character describedwhich can be chosen to be non-toxic and to eliminate any noxious orunpleasant aspects in its formulation, application to a substrate, useand developing. It is yet another object to provide such a system whichcan be made extremely light-fast, which is flexible with respect to themanner in which it may be exposed, to the type of processing to which itis subjected and to the type of final product achieved.

It is another primary object of this invention to provide a method ofphotography or photocopying which is capable, through the choice of dyesand structure of the lightsensitive system, of producing prints ortransparencies in black-and-white, monochrome or full color which areextremely light-fast and which may be applied to cloth as well as topaper substrates.

It is another primary object of this invention to provide protosensitivearticles of the character described and methods of using them which aresimple to formulate and use and which may be relatively inexpensive.Other ob jects of the invention will in part be obvious and will in partbe apparent hereinafter.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others, and thearticle possessing the features, properties, and the relation ofelements, which are exemplified in the following detailed disclosure,and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is a cross section of the light-sensitive system of thisinvention applied to a substrate;

FIG. 2 illustrates the step of exposing the photosensitive sheet of FIG.1 to a negative for copying by direct contact;

FIG. 3 illustrates the formation of the image made by the exposureillustrated in FIG. 2;

FIG. 4 illustrates the use of the photosensitive article of thisinvention to make a reverse copy of an opaque original by the reflextechnique;

FIG. 5 illustrates the copy made by the exposure illustrated in FIG. 4;

FIG. 6 illustrates the use of the photosensitive article of thisinvention to make a right-reading copy of an opaque original by thereflex technique;

FIG. 7 illustrates the use of the photosensitive article of thisinvention to make a right-reading copy of an opaque original by theprojection technique;

FIG. 8 illustrates in cross section one embodiment of a film suitablefor producing full color prints or transparencies in accordance withthis invention;

FIG. 9 illustrates in cross section another embodiment of film for fullcolor;

FIG. 10 illustrates diagrammatically the result of exposing the film ofFIG. 8 to white light through a transparency which is red, green, andblue; and

FIG. 11 illustrates diagrammatically the effect of projecting whitelight through the exposed and fixed film of FIG. 10.

The photosensitive positive bleach-out system of this invention may bedefined as one which comprises an indigoid dye such as an indigo,thioindigo, or selenoindigo dye, or a combination of such dyes and anactivator which is a colored photo-reducible dye. More specifically,these activators are compounds which are reduced when exposed to apredetermined wavelength range of the electromagnetic spectrum. In thecase of the systems of this invention this wavelength range generallyencompasses the normally visible light wavelength range. Some of thesystems are also bleached by ultraviolet light.

The bleach-out dyes usable in the photosensitive system of thisinvention may be generally defined as the indigoid dyes which includethe indigo and indirubin dyes. These dyes have long been known as veryintense, stable, and extremely light-fast dyes. The indigoid dyes,moreover, otter a wide range of colors as well as the possibility of aone-dye black, this latter being particularly attractive for a photocopysystem.

The term indigoid dye as used hereinafter is meant to include all thosedyes generally considered by those skilled in the art to fall within thegeneral class of dyes having as their chromophoric structure theconjugated grouping which is reducible to the substantive leuco form. Asubstantial body of art exists on the synthesis, classification, andnaming of these indigoid dyes. (See for example The Chemistry ofSynthetic Dyes by K. Ven'kataraman, Academic Press, Inc., New York,1952, pp. 10034045; and Colour Index second edition, 1956, volume 3published in the United States by the American Association of TextileChemists and Colorists, pp. 3547-3567.)

There are a number of ways in which the indigoid dyes may be classifiedand described. The following brief description represents one way ofgrouping these dyes in subclasses better to illustrate the variousstructures possible. These subclasses and the examples given are meantto be illustrative and not limiting.

(1) Symmetrical derivatives of indigo, thioindigo and selenoindigorepresented as wherein R may be one or more of the following: loweralkyl, lower alkoxy, Cl, Br, NH NaSO aryl and substituted aryl. Anexample of this subclass is which is known as C.I. Vat. Blue 41 and isreddish blue in color.

(2) Asymmetrical derivatives of indigo, thioindigo or selenoindigorepresented as wherein X and Y are different and may be one or more ofthe following: lower alkyl, lower alkoxy, Cl, Br, NH NaSO aryl, andsubstituted aryl. An example of this subclass is use? o which is knownas Cil. Vat Red 6 and is bright red in color.

(3) Indirubins represented as which is known as Ciba Heliotrop B and ismagenta red in color.

(4) Indigos and indirubins wherein one imino group is replaced by sulfurrepresented as R2 and wherein R and R may be the same or difierent andare one or more of the following: lower alkyl, lower alkoxy, Cl, Br, NHNaSO aryl and substituted aryl. Two examples of this subclass ofindigoid dyes are H O I H which is known as C.I. Vat Violet 5 and isbluish violet in color; and

which is known as Algol Brown GN and is dull yellowish orange in color.

(5) Dyes containing one ketone-bearing heterocyclic grouping connectedby means of a double bond to a carbon alpha to a keto or 0x0 group in anaromatic system as represented by wherein R R and R which may be thesame or different, are one or more radicals which may be lower alkyl orhalide. An example of this subclass of indigoid dyes is (FREQ themselvesdyes-namely those dyes well known in the art as photoreducible dyes (seefor example Light- Sensitive Systems by Jaromir Kosar, John Wiley &Sons, Inc., New York, 1965, pp. 184-187). These dyes are known toundergo reduction to their leuco form in the presence of electron donorswhen exposed to visible light. The term photoreducible as usedhereinafter is also meant to include phenanthrenequinone andanthraquinone and their derivatives which in the dye-activator systemsof this invention appear to behave as photoreducible dyes. Forconvenience these are all referred to as photo reducible dyes, theirfunction being to cause bleaching of the image dye under the radiationused, e.g., visible light. However, the actual mechanism by which thisis accomplished is not precisely known.

In general the following classes of dyes are included in the activatordyes of this invention:

(1) The thiazines of the general formula wherein X is an acid anion Yand Z are exemplified, but not limited to, one or more of the following:H, alkyl, substituted alkyl, aryl, substituted aryl, benzo, substitutedbenzo, -0 SO Cl, Br, I, OR, NRIR',

- 3oR and fi-NRR wherein R and R may, for example, be H, alkyl,substituted alkyl, aryl or substituted aryl;

(2) The thiazoles of the general formula where Z has the same meaning asin the thiazine class and R and R may be, for example, H, alkyl,substituted alkyl, aryl or substituted aryl and R may be omitted;

(3) The acridines of the general formula fea R X wherein R, Y and Z arethe same as in the thiazines and W is the same as Y and Z;

(4) The azines and oxazines of the general formulas wherein R, Y and Zhave the same meanings as they do in the thiazine class;

(5) The anthraquinones of the general formula wherein Y and Z have thesame meaning as in the thiazine class and in addition may be SO H, SH,

NO or a ring residue of a 5- or 6-membered heterocyclic ring;

(6) The phenanthrenequinones of the general formula wherein Y and Z havethe same meaning as in the anthraquinone class;

(7) The xanthenes (A) of the general formula Z l W wherein R has thesame meaning as in the xanthenes (A) and W and Z may be exemplified, butnot limited to, alkyl, substituted alkyl, aryl, substituted aryl, --SR,

COOR, NO --Cl, Br, and I.

The following list of photoreducible dyes illustrates specificactivators which may be used with the bleach-out dyes to form thephotosensitive system of this invention. This list is meant to beillustrative and not limiting:

acid violet acridines (red, orange and yellow) acriflavine Azure Bbenzoflavine chromogen red B chromoxane brilliant red coeruleinfluorescein and its naphthalene analog gallein hexahydroporphinmercurochrome methylene blue negrosine C phenosafranine phloxinepyronine G riboflavin rivanal phenanthrenequinone quinalizarinrhodamines (B, S and G) rose bengal safranines (O, T) sulforhodamine Bthioflavine T thionin toluidine blue 0 In the forming the photosensitivesystem of this invention, the mole ratio of activator to dye may rangefrom about 0.0l-to-1 to about 10-to-1, with about 1-to-1 being typicaland generally preferred. The activator-dye ratio employed will, ofcourse, depend upon the activator-dye system as well as upon theperformance characteristics desired from the photosensitive system.

In compounding the photosensitive composition, it may also be desirableto incorporate one or more additives. For example, such additives mayinclude, but are not limited to, plasticizers, agents to control thecoating properties, and compounds capable of filtering specificwavelengths, particularly ultraviolet. In addition, encapsulated fixingprecursors may be included for mechanical release (e.g., application ofpressure to break the capsules) after exposure.

The photosensitive system (dye plus activator) is alfixed to a substratethrough a film-forming binder. This is most conveniently done by forminga solution of the binder along with any additives such as plasticizers,etc., in a suitable solvent and then adding the dye and activator to thesolution under conditions of temperature and exposure to light whichwill not effect any premature bleaching of the dye. The film-formingbinder must not, of course, have any adverse effects on the ability ofthe desired electromagnetic radiation to bleach the dye.

The role of the binder in forming a suitable photosensitive system isnot completely understood; but it appears that it is desirable to use abinder having the structure incorporated therein where X is anelectronegative element. Perhaps such binders donate a hydrogen atom, apossibility if the CH bond is of the type which is relatively easilybroken. A suitable binder can be easily chosen as a result of simpleexperimentation with the desired dyeactivator combination. If oxygenenters into the activation process when the photosensitive system isexposed, then it is preferable that the binder be oxygen-permeable.

A number of film-forming resins may be used as the binder; and thepreferred one is nitrocellulose applied as a solution in acetone. Othersuitable binders include, but are not limited to ethyl cellulose,polystyrene, polymethyl methacrylate, and cellulose acetate butyrate.Solvents will be chosen which are compatible with these binders, andtypical solvents include, but are not limited to, acetone, toluene,methylene chloride, and mixed solvents such as toluene/tetrahydrofuranand benzene/acetone. The performance of the photosensitive systemdeposited in binders other than nitrocellulose may be enhanced in somesystems if a precoat intermediate layer of nitrocellulose is interposedbetween the substrate and the photosensitive layer. The reason for thisenhancement is not understood but may be evidenced by an increase inbleaching speed.

The concentration of the dye and activator in the solution of thefilm-forming material will be governed by the final coating Weightdesired and the technique used to apply the coating solution to thesubstrate surface. The coating weight in turn will generally determineboth the image quality and speed of the photosensitive system. Ingeneral, the lighter the coating weight the higher will be theresolution and the faster will be the bleaching. The optimum coatingweight will also depend upon the extinction coefficient of thephotosensitive system and will generally range between about 1x10" toabout 1x10- gram dye per square centimeter.

Typically, the concentration of the dye in the coating solution mayrange from about 0.01 gram per milliliters to the limit of thesolubility of the dye in the solution. The amount of activator presentwill, of course, be governed by the selected mole ratio of activator todye as defined above.

The thickness of the liquid coating at the time of application to thesubstrate may vary over a wide range and will be governed by the finalcoating weight desired, the solids concentration of the coating solutionand the method by which the coating as accomplished.

The coating composition may be applied to the substrate by any suitable,Well-known coating techniques including roller coating, spraying,brushing, knife coating, and the like. Coating and drying must, ofcourse, be accomplished under conditions which will not cause anypremature bleaching of the dye, preferably in subdued light or byillumination of a safelight.

The substrate material will, of course, be chosen to give thecharacteristics desired in the final photograph or photocopy and suchmaterials are Well known in the art. Thus, for example, if prints orphotocopies are desired, the substrate will be an opaque paper material,typically a photographic print paper. If on the other hand the finalproduct is to be a transparency, then the substrate will be atransparent film, typically of a synthetic resin. The substrate may beflexible or nonfiexible as desired, and if a protective or barrier filmis interposed between the substrate and the photosensitive film, littleattention need be given to the chemical characteristics of thesubstrate.

The interposition of an intermediate layer between the substrate and thephotosensitive film may be desirable for one or more of a number ofreasons. This intermediate layer of a material capable of absorbinglight within a used for forming the photosensitive layer or it may beformed of any other suitable type of material. It may serve as a barrierto prevent unwanted chemical components of the substrate from makingcontact with the photosensitive layer may be a coating of the samefilm-forming material the physical properties of the substrate such asto render it smooth, make it more adhseive to the coating solution, orprevent curl of the substrate. The intermediate layer may also be usedto enhance the optical properties of the photosensitive articleconstructed in accordance with this tion layers which are well known inthe art and/or a layer. The intermediate layer may also be used toenhance given wavelength range.

FIG. 1 illustrates, in diagrammatic cross section, a photosensitivelayer. As examples we may cite antihalainvention. Such an articlenormally takes the form of sheet formed of a substrate 11, anintermediate layer 12, and a photosensitive layer 13. The article ofFIG. 1 would be particularly suitable for making two-color copies ortransparencies, depending on the characteristics of the substrate 11.Thus, if the substrate 11 is an opaque sheet, the final result will be aphotocopy or a print, while if the substrate 11 is, for example, atransparent film, th final copy will be a transparency. As explainedabove, the intermediate layer 12 is optional and may be used to performone or more of several functions. Similarly, the photosensitive layer 13may be covered, such as with an anti abrasion coating 18.

FIG. 2 illustrates the manner in which a photosensitive sheet such asthat shown in FIG. 1 may be used to form a copy of a transparency havinga light or transparent background 15 and indicia 16. The photosensitivesheet 10 with the photosensitive layer 13 (shown in FIG. 2 at theinitiation of exposure) in contact with the transparency 14 is exposedto a suitable light source, generally in this case a source 17 of lighthaving high visible output at the Wavelength absorbed by thephotosensitive system. The light from source 17 (e.g. a SOD-wattphotofiood lamp) will, of course, be transmitted through the light orcolorless areas 15 of the transparency to strike the photosensitivelayer 13 and to bleach-out the dye in those areas which are thus exposedto leave the colored activator. However, since the light is not capableof being transmitted through the dark or black areas of indicia 16,these areas remain the color of the original dye activator systeminasmuch as no bleaching has occurred. The result is the copyillustrated in FIG. 3 wherein the numeral 20 designates the dye-bleachedareas now the color of the activator corresponding to the light areas ofthe negative used. Areas 21, corresponding directly to the indicia onthe transparency, remain the color of the original dyeactivatorphotosensitive system. The result is a two-color print.

The production of a reverse-reading copy of an opaque master isillustrated in FIGS. 4 and 5. The photosensitive sheet is placed suchthat the photosensitive layer 13 contacts the opaque master formed ofwhite background areas 23 and dark indicia 24. Exposure to strongvisible light will result in its reflection from the white background 23against the photosensitive layer to produce a dyebleached area 26 (FIG.5) and unbleached areas 25.

FIGS. 6 and 7 illustrate diagrammatically two ways in whichright-reading copies may be made directly either by the reflex technique(FIG. 6) or the projection technique (FIG. 7). In FIG. 6 thephotosensitive sheet is placed with the substrate surface in contactwith the opaque master. Under these circumstances, some definition ofoutline is lost, but it is satisfactory for some purposes. In FIG. 7 thevisible or other light from source 17 is directed through suitablewell-known projection optics indicated at 18 to strike the original andto be reflected from the white or light areas 23 onto the photosensitivelayer 13. This technique is quite feasible using visible light since theprojection optics are relatively easy to design and inexpensive toconstruct.

In order to be able to store the copies of FIG. 3 over an extendedperiod of time and to use and handle them in the normal daylight, it isnecessary to inactivate or fix the activator within the unbleachedareas. A number of types of fixin steps may be employed, depending uponthe characteristics of the activator, the overall dye system, and themanner in which the copy is to be used.

The fixing may be accomplished through one of several routes, includingthe destruction of the activator, removal of the activator, or byquenching of the system.

As noted previously, materials may be added to the photosensitivecoating compositions, one of these being extremely small capsules whichmay be broken mechanically (such as by passing through the nip of tworollers) to liberate the encapsulated chemical. If a reducing agent forthe activator is contained within such capsules, fixing may beaccomplished by breaking them to free the re ducing agent within theexposed photosensitive layer. This method offers the possibility ofrapid, dry fixing.

After the initial exposure to form the image in the photosensitivelayer, an overcoating containing a reducing agent for the activatorwhich decolorizes it may be applied. Exposure to further radiationcompletes the fixing. Such further exposure may be efiected through theuse of a high intensity light source or of room light, the choicegenerally being the rapidity with which fixing is to be one.

A third way of fixing is to apply a solvent for the activator to theexposed photosensitive layer to remove the activator. The solvent must,of course, not be a solvent for the indigoid dye.

Finally, certain dye-activator systems may be fixed with ultravioletlight if the system is of a type which can be imaged with visible lightand the activator is of a class which can be photochemically reduced byultraviolet light. (See for example Photopolymerization Studies: II.Imaging and Optical Fixing in Photographic Science and Engineering 12,177-184 (July-August 1968).)

The following examples, which are meant to be illustrative and notlimiting, are given further to describe the invention.

Example 1 Suificient acetone was added to a mixture of 10 g.nitrocellulose (Hercules RS5-6 seconds wet with 30% by Weight isopropylalcohol) and 5 g. of dibutylphthalate (plasticizer) to make g. of astandard binder solution. A casein-coated, smooth finish paper wascoated with a 2-mil wet thickness film of this standard binder solutionand dried. This precoated paper was used in all of the examples.

To 15 ml. of the above standard binder solution were added 2.5 ml.acetone, 5 ml. of a dye solution (formed by dissolving 0.058 g. ofN,N'-dimethylindigo in 50 ml.

acetone) and 0.017 g. eosin YB. A 6-mil wet thickness was coated on theprecoated paper and driedthe entire process of mixing, coating anddrying being carried out under subdued light.

The photosensitive sheet was exposed for minutes through a 21-step KodakPhotographic Step Tablet (No. 2 with a density range 0.05 to 3.05) and aglass plate to a source of illumination at a distance of inches. In theuse of this standard device for measuring photosensitivity the number ofsteps which have a discernible lower density than the unexposed portionof the photosensitive layer is a measure of its photosensitivity. Thismeans, of course, that the greater the number of steps, the greater isthe sensitivity of the system.

When the source of illumination was a 500-watt reflector photofloodlamp, 9 steps were bleached. In the absence of any of the eosinactivator, no bleaching occurred.

FIG. 8 illustrates diagrammatically one structural embodiment of aphotosensitive film suitable for making color copies as prints ortransparencies. The photosensitive layer assembly 30 is affixed to anopaque or transparent substrate 31. The photosensitive layer assemblycomprises, from top down, a photosensitive layer 32 having a yellow dyewhich is bleached by blue light in the presence of a yellow coloredactivator; a barrier layer 33; a photosensitive layer 34 having amagenta dye which is bleached by green light in the presence of amagenta colored activator; a barrier layer 35; a photosensitive layer 36having a cyan dye which is bleached by red light in the presence of acyan colored activator; and an antihalation layer 37. One or more of thebarrier layers and/ or the antihalation layer may be omitted, dependingupon the characters of the dyes and activators, e.g., whether theyinteract or migrate from layer to layer, etc.

There are a number of dye-activator combinations which may be used. Asexamples, we may cite Ciba orange as dye with acridine yellow as theactivator for the yellow dye-activator layer; N,N'-diacetylindigo witherythrosin or eosin as the activator for the magenta dyeactivator layer;and N,N'-dimethylindigo with methylene blue or thionin as the activatorfor the cyan dye-activator layer.

The barrier layers may be of any suitable material which does notinterfere with the transmission of radiation, i.e., a thin film ofnitrocellulose. They may also be layers of a material having a chargeopposite to that of the activator, of a material which is a mordant forthe activator dye system, or of a material through which the activatordye diffuses very poorly. Finally, as a substitute for or in addition tothe barrier layers, the activator dye may be rendered nonwandering byattachment of a macromolecule. Antihalation layers are well known in theart. See for example Photographic Chemistry by Pierre Glofkides,Fountain Press, London, 1958, volume 1, page 470 et seq.

FIG. 9 illustrates another structural embodiment of a photosensitivefilm in which like numbers refer to like elements in FIG. 8. In thestructure of FIG. 9 the photo sensitive layer assembly consists of twosections-section 30a adhered to one surface of the substrate 31 andsection 30b adhered to the other surface of the substrate. Thisarrangement is, of course, only suitable if substrate 31 is atransparent film. It has, however, the advantage of offering thepossibility of eliminating one barrier or antihalation layer. It alsooffers more flexibility in fixing processes, allowing different forms offixing techniques to be applied to the two separated sections 30a and30b. The actual arrangement of dyes and activators is also flexible andneed not be that shown in FIG. 9.

FIG. 10 illustrates the manner in which the photosensitive layerassembly of the film functions when exposed to blue, green and red lightgenerated by a suitable transparency 40. The film of FIG. 10 has anadditional top layer 41, the function of which is to absorb ultravioletradiation. It may or may not be strippable and is optional, its usebeing dependent upon whether or not it is necessary to prevent unwanteddye bleaching by ultraviolet light. In FIG. 10 it will be seen that thearea 42 exposed to blue light absorbs blue and is bleached; the area 44absorbs green and is bleached; and the area 46 absorbs red and isbleached. Since the system is a subtractive color system, when whitelightis passed through the exposed film, the area corresponding to area42 (FIG. 11) will transmit blue, that corresponding to area 44 willtransmit green and that corresponding to area 46 will transmit red.

The use of the indigoid dyes in a bleach-out system provides thepossibility of forming intensely colored, lightfast images not only in alayer of a photosensitive coating applied to the usual substrates, e.g.,films or papers but also within the substrate itself. Thus, cloth orfabric may be impregnated with the photosensitive composition to formdye images in situ in the fabric. Indigoid dyes with suitable activatorsalso provide the possibility of making a one-dye black system.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in carrying out the above method andin the article set forth without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

We claim:

1. A photosentitive composition which bleaches to form an image uponexposure to visible or ultraviolet radiation, comprising in combinationan indigoid dye having the conjugated grouping O l l and an activator ina binder, said activator being a colored photoreducible dye capable ofbleaching said indigoid dye when exposed to a predetermined wavelengthrange of electromagnetic radiation in the presence of said activator andselected from the group consisting of thiazines, thiazoles, acridines,azines, anthraquinones, phenanthrenequinones and xanthenes.

2. A photosensitive composition in accordance with claim 1 wherein saidindigoid dye is a symmetrical derivativt of indigo, thioindigo orselenoindigo.

3. A photosensitive composition in accordance with claim 1 wherein saidindigoid dye is an asymmetrical derivative of indigo, thioindigo orselenoindigo.

4. A photosensitive composition in accordance with claim 1 wherein saidindigoid dye is an indirubin.

5. A photosensitive composition in accordance with claim 1 which isactivated by visible light.

6. A photosensitive composition in accordance with claim 1 wherein themole ratio of activator to dye ranges between about 0.01-to-1 to aboutIO-to-l.

7. A photosensitive composition in accordance with claim 1 wherein saidbinder incorporates the structure wherein X is an electronegativeelement.

8. A photosensitive composition in accordance with claim 1 wherein saidbinder is nitrocellulose.

9. A photosensitive composition in accordance with claim 1 wherein saidbinder is ethyl cellulose.

10. A photosensitive composition in accordance with claim 1 wherein saidbinder is cellulose acetate butyrate.

11. A photosensitive composition in accordance with claim 1 wherein saidbinder is polystyrene.

12. A photosensitive composition in accordance with claim 1 including anadditive which is a radiation filtering material or an encapsulatedfixing agent.

13. A photosensitive article suitable for exposure to radiant energy forforming an image by direct bleach-out, comprising in combination (a) asubstrate; and

(b) a least one layer of a photosensitive composition atfixed to saidsubstrate in a binder, said photosensitive composition comprising incombination (1) an indigoid dye, and (2) an activator which is a coloredphotoreducible dye capable of bleaching said indigoid dye when exposedto a predetermined Wavelength range of visible or ultraviolet radiationin the presence of said activator and is selected from the groupconsisting of thiazines, thiazoles, acridines, azines, anthraquinones,phenanthrenequinones and xanthenes.

14. A photosensitive article in accordance with claim 13 furthercharacterized by having an intermediate coating layer interposed betweensaid substrate and said layer of said photosensitive composition.

15. A photosensitive article in accordance with claim 13 characterizedby having a plurality of photosensitive layers each of which comprises aphotosensitive com position being sensitive to light of a wavelengthdifferent from the wavelength to which any other of said compositions issensitive, whereby said article is capable of forming multicoloredimages upon exposure.

16. A photosensitive article in accordance with claim 15 wherein saidlayers are separated by layers of nonphotosensitive material.

17. A photosensitive article in accordance with claim 15 wherein atleast one of said plurality of photosensitive layers is on one surfaceof said substrate while the remaining of said layers are on the othersurface of said substrate.

18. A method of forming an image of a master by direct bleach-out,characterized by exposing a photosensitive system in association withsaid master visible or ultraviolet radiation of a predeterminedwavelength range, said photosensitive system comprising in combinationan indigoid dye and an activator incorporated in a binder and beingaffixed to a substrate, said activator being a colored photoreducibledye capable of bleaching said indigoid dye when exposed to saidradiation and being selected from the group consisting of thiazines,thiazoles, acridines, azines, anthraquino-nes, phenanthrenequinones andxanthenes.

19. A method in accordance with claim 18 further characterized by thestep of fixing said image, wherein aid fix-ing comprises destroying saidactivator by applying to said image a reducing agent for said activator.

References Cited UNITED STATES PATENTS 1,850,220 3/1932 Wendt, et al.96-89 2,163,094 6/1939 Kambli 8-28 3,154,416 10/1964 Fidelman 9689X J.TRAVIS BROWN, Primary Examiner J. WINKELMAN, Assistant Examiner US. Cl.X.R. 96-73, 89

